1. Field of the Invention
The present invention generally relates to an actuator structure and a recording-reproducing apparatus, and more particularly, to an actuator structure which is capable of moving a head for recording and/or reproducing information to a predetermined position of a recording medium and a recording-reproducing apparatus provided with such an actuator structure.
2. Description of the Related Art
Recently, a recording-reproducing apparatus such as a magnetic disk apparatus has been downsized and its capacity has been increased. Due to the increase of its capacity, in particular, TPI (track per inch) has also increased and so a track pitch has narrowed. For this reason, demands have been increased for a high-speed seek and a high-accuracy positioning.
FIG. 1 is a plan view of an actuator portion of a conventional magnetic disk apparatus 11. FIG. 2 is a cross-sectional view of the actuator portion shown in FIG. 1. In FIGS. 1 and 2, a predetermined number of magnetic disks 13 (two in FIG. 2) are rotated by a spindle motor (not shown) in a base 12 of the magnetic disk apparatus 11. A magnetic head 14 is moved in a radial direction by an actuator 15 on each surface of the magnetic disks 13.
The actuator 15 is comprised, integrally, of a rotary shaft 18, which is formed by a shaft 16 and bearings 17, and arms 19, a number of which corresponds to a number (of recording surfaces) of the magnetic disks 13, provided for each of the magnetic disks 13. A gimbal 20 is fixed to a tip of each of the arms 19 and the magnetic head 14 is formed on each of the gimbals 20 so as to oppose each recording surface of the magnetic disks 13.
On the other hand, two coil support portions 21a and 21b are integrally and symmetrically formed on the other side of the magnetic disk 14 and a voice coil 22 is fixed to a U-shaped end portion formed by the coil support portions 21a and 21b using an adhesive 23. The voice coil 22 is formed by winding the coil a predetermined number of times.
A magnet 25 fixed to a yoke 24 is provided above the voice coil 22 and a magnet 27 fixed to a yoke 26 is provided underneath the voice coil 22. Each of the magnets 25 and 27 is placed so that opposed polarities face each other. Studs 28a and 28b covered by rubber members 29a and 29b, respectively are provided at left and right sides of the yokes 24 and 26. Each of the rubber members 29a and 29b, respectively, functions as a stopper which contacts the coil support portion 21a or 21b when the actuator 15 rotates around the rotation shaft 18. In addition, the numeral 30 indicates an FPC (flexible printed circuit) which supplies current to the voice coil 22 and send/receive signals to/from the magnetic head 14.
FIG. 3 is a cross-sectional view of another conventional actuator structure. In FIG. 3, a cradle 21c for the voice coil 22 is provided at a lower portion between the coil support portion 21a and 21b. The cradle 21c is formed of, for example, a resin or an aluminum plate, and fixed by bolts. Other configurations are the same as the ones shown in FIG. 2. The cradle 21c prevents a generation of resonance during a driving of the actuator 15 (during power supply to the voice coil 22) by enhancing a fixation state of the voice coil 22.
The reason that the voice coil 22 is supported by the coil support portions 21a and 21b at each end is to improve an accuracy of positioning, seek speed, etc., since the track pitch is shortened due to a high TPI associated with a high-capacity magnetic disk apparatus. Also, the doughnut shape of the voice coil 22 contributes to minimize inertia.
However, if the thickness of the above-mentioned coil support portions 21a and 21b is reduced in order to achieve a weight reduction, their rigidity will be also reduced and torsional vibration will be caused during an operation of the disk apparatus. Especially, since the coil support portions 21a and 21b are symmetrically formed, they tend to help or enhance the torsional vibration. Once this vibration is transferred to the magnetic head 14, it is difficult to carry out a positioning with high accuracy.
Also, as shown in FIG. 1, since lines from both ends of the side 22a.sub.1 to the shaft 16 (rotation center) are deviated from the lines 22b.sub.1 and 22b.sub.2, respectively, efficiency of the magnetic circuit is not very good. Thus, more power is consumed and the high-speed seek and accurate positioning are influenced by such factors.
Moreover, to provide the cradle 21c in order to decrease the resonance during the operation of the above-mentioned coil support portions 21a and 21b causes widening of an air gap of the magnetic circuit formed by the voice coil 22, magnets 25 and 27, and yokes 24 and 26. Thus, sufficient magnetic flux density cannot be obtained and the efficiency of the magnetic circuit is lowered. Also, problems such as a high cost due to an increased number of parts and an increased number of construction steps are caused.